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Things to consider

Why are window and doors important and how do you make the right choice?

Choosing the right windows and doors has a significant impact on heating and cooling bills, as well as on maintenance. Aside from being the link between indoor and outdoor living, they also contribute significantly to the look of the building as well as providing controlled ventilation.

There are a number of performance measures that will determine the comfort and energy consumption of the window or door in use. Choosing and comparing windows & doors you should be prepared to ask the right questions and more important be able to evaluate the quality of the answer.

Approximately 30-50% of heat loss of a building is through the windows and doors.

Approximately 80-90% of solar gain of a building is through the windows and doors.


What are the important factors for you when choosing window and doors?

Design and Appearance

  • Do you have the freedom to customise the windows & doors – the sizes, shapes, glass, colours and extras (e.g. handles, locks etc.)?
  • Does the design influence the performance of the window?

With Eurotech WinDoors windows and doors you can individualise the look of your home, create an eye catching house and achieve a perfect balance with your overall building design.

Tip: The design options should give you the freedom to choose without influencing the performance.

Costs & Maintenance

What are the costs over the life cycle – maintenance and energy (e.g. heating & cooling savings)?

  • What is the life expectancy of the product?

Keep in mind that windows & doors usually remain in your house for at least 25 years. Solid wooden windows and doors are long term investments when maintained correctly and they are more economical than their artificial alternatives if use periods are taken into consideration.

Don’t forget to consider performance as a cost factor – quality hardware and seals should ensure a long life expectancy.

Tip: Ratings show you the performance of your new product. They don’t necessarily incorporate the quality of hardware and seals (gaskets) for ongoing durability. Check the hardware and seals for functionality.
The best way is to touch and see.


  • How is the window rated?
  • How does the window perform over its lifetime?
  • What are the performance measures that show the value of the product?
  • What is the life expectancy of the windows?

The discerning customer will invest in quality windows.

As well as performance, maintenance and handling you should always consider the environmental impact of your choice.

Tip: The rating is just a snapshot in time. Always ask for the value and constancy of the performance over time. Including various aspects in your decision is important. The bitterness of poor quality lingers on long after the sweetness of a low price.

Is double glazing mandatory?

No. New Zealand Building Code has performance requirements in the 3 NZ climate zones for new builds with double glazing being the easiest method of obtaining these.

Tip: Only double or triple glazing offers a convenient comfort and security level all year round.


Is double glazing enough?

No. Double glazing is only one component that contributes to the performance. The frame, gaskets and hardware as well as the level of craftsmanship influence the quality and performance of the product

Tip: Windows and Doors are a long term investment – see & touch the whole product before you make a decision.


Is it easy to compare windows?

No. The performance measures are a good indicator, but they only show a fraction of the window quality level. Sustainability of components, value over life cycle and functionality are not represented by generalised values & ratings.

Tip: You really should make sure that you compare apples with apples


Are performance values important?

Yes. The performance measures should be your minimum requirement, but always check if they apply for the whole window (not just for one component) and if it’s applicable in real life. The Rating (WERS) is a computer simulated testing. In regard to the frame the system disadvantages timber to aluminium. This leads to inaccurate and distorted values.

Heat Loss - Winter Heating

“30-50% of the buildings heat loss is through the windows and doors.”

Heat loss is usually caused by poor insulation in winter and is the opposite of heat gain caused by poor insulation in summer.

Usually the windows and doors are a weak part of the building. Aluminium-only frames and non-efficient glass cause the major amount of heat loss. Walls and roof usually contain timber and other materials that have a low conductivity and help to insulate.

You can save energy, every day. The right choice lowers your operational costs and increases your comfort levels at the same time.

The benefits of Eurotech WinDoors whole-of-window insulation are:

  • improved comfort all year round
  • reduced heating and cooling of around 40%
  • saves non-renewable resources and reduces greenhouse gas emissions
  • reduced condensation on walls and ceilings
  • noise reduction

Heat Gain

“80-90% of solar gain of a building is through the windows and doors.”

Heat Gain is caused by poor insulation in summer. Aluminium-only frames and non-efficient glass cause the major amount of heat gain. Walls and roof usually contain timber and other materials that have a low conductivity and help to insulate and windows & doors remain as the weak part of the building.

Heat Gain can occur in three ways:

  1. Solar Heat Gain
  2. Air Infiltration (AI)
    Siphons about half of an average home’s heating and cooling energy to the outdoors. Air leakage through and around windows is responsible for much of this loss. Advanced sealing with compressible gaskets and tight hardware reduce air leakage and heat gain in summer through air movement.
  3. Conductive Heat Gain
    Is movement of heat through a material. Aluminium is highly conductive (237 K) compared to timber (0.16 K – oak). Low conductive glass, such as double glazing with minimum air gap of 16mm and low conductive frame, like timber and timber-aluminium, minimise conduction.

You can save energy, every day. The right choice decreases your operational costs whilst increasing your comfort levels at the same time.


Every component plays a part in the performance of the windows and doors. Heat gain and loss occur due to conduction, convection, radiation and air leakage.

The U-Value of a window describes transfer of heat by conduction, convection and radiation.

The R-Value is the inverse to this. U is the flow of heat and R is the resistance to flow.

Tip: Window manufacturers try to advertise a low U-Value (high R-Value). Be careful. This may only be the value at the centre of the glass (Ug). Don’t settle for high glass values. Look for “whole-window” values (Uw). U-values influence heat loss more in cold climates because the difference between indoor and outdoor temperature is much higher than in hot climates.

The Air Infiltration and the U-Value are comprehensive measures to value the thermal performance of a window. By following the guidelines and including elevation and climate into your project plan for windows & doors, you will be able to achieve a comfortable and energy efficient result.

Important: The values are only one aspect of the product quality. An intelligent choice includes environmental aspects, life cycle assessment, life expectancy and operational comfort.

Condensation Resistance (CR)

CR measures the ability of a product to resist the formation of condensation on the interior surface of the product. Condensation, which can appear as a light coating of water, water droplets, frost, ice, or some combination of the four, forms on any surface when the temperature of that surface is less than its dew point temperature. For example, if the temperature of the glass in a window is 10°C and the dew point temperature for the glass is 12.5°C, condensation will form on the surface of the glass.

The rating recognizes three parts to a window: the centre-of-glass; the edge-of-glazing; and the frame. High conductive parts of the window are the least energy efficient, causing lower indoor surface temperatures and condensation. To reduce the potential, each component of the window should be thermally efficient. The CR is expressed as a number between 0 and 100. The higher the rating, the better it resists condensation formation.

How do you increase the condensation resistance?

To increase the resistance of windows to the formation of condensation, it is important to maintain the surface temperature of the window above the dew point.

Eurotech WinDoors reduce the potential for condensation by targeting areas of potential temperature variation:

Centre-of-glass & Edge-of-Glass by only manufacturing with high performance double glass options with a 16mm gap between panes. Further improved, by choosing energy-efficient, low-e or shading options.

Frame – By using low conducting timber frames instead of highly conductive metal framing.

Single glazing and aluminium-only frames are more likely to suffer from condensation. Fungal decay and rotting can be the result.

Visible Transmission (VT)

VT is the transfer of light of visible wavelength. VT is usually expressed for the whole window, but the important value is the one for the glass.

A high value of visible transmission brings in daylight and reduces the need for artificial light in your home or office.

The visible transmission should be evaluated for each project. Depending on climate area, elevation and available natural (e.g. trees) and artificial (e.g. blinds & curtains) shading options each project has its own requirement.

Increasing the visible transmission in cold climates can be beneficial. It can reduce the need to artificial lighting. Keep in mind that thermal performance might have an impact on your choice as well.

In hot climates improved shading might create a higher comfort. It can be beneficial to use the shaded glass option to reduce light transmission and heat gain to lower cooling costs and unwanted bright indoor environment. The available glass options can also help to reduce the impact of fading (discolouration of curtains, carpet etc.)

Glass options and sizes of windows and doors influence the performance.

Glass coatings are available in different colours. Grey and green are the typical choices.

Keep in mind that elevation, climate and landscape you live in, as well as the looks, should influence your decision.

There is no general rule. It is important to find the right solution to match your requirements.


Life Cycle Assessment (LCA)

LCAs are the modern approach to calculate the environmental impact and the overall value of a product. The assessments are usually very complex and sophisticated.

It is difficult to supply complete results because to calculate the life cycle value of a product all components and their interaction have to be valued over all stages of a product’s life.

Beginning with sourcing and manufacturing. Followed by Installation, Usage and end-of-life aspects.

There is no standard for these assessments.

The main targets are:

  • sustainable sourcing of used materials (like timber)
  • efficient manufacturing and administration
  • long term energy efficiency
  • low maintenance
  • long life cycle
  • recyclable and reusable product & components
  • reduced impact of transport at any stage of the life cycle